1. Field of the Invention
The present invention relates to a seat back for a vehicular seat.
2. Description of the Related Art
The seat back for the vehicular seat generally includes a seat back frame and a pad. Moreover, the seat back of the type having a thin pad further includes a plate member for supporting the back of the pad, and an elastic support mechanism for holding the plate member elastically and movably forward and backward relative to the seat back frame. One example of a plate member is disclosed in U.S. Pat. No. 6,296,308 (308 patent), for example.
Here, the thoracic vertebrae of a user seated on a vehicular seat are bent to bulge toward the seat back. Moreover, the seat back of the thin pad type has a tendency for the plate member to apply a strong pushing force to the thoracic vertebrae. This can result in a more uncomfortable ride. For example, the plate member disclosed in FIG. 2 of the 308 patent applies a strong pushing force to the thoracic vertebrae with the portion of the plate member matching the thoracic vertebrae. The plate member disclosed in FIG. 10 of the 308 patent has a slot at the widthwise center, but this slot is less wide than the thoracic vertebrae as it is considered that a sitting position is not always at the center of the seat's width. As a result, this plate member also applies the strong pushing force to the thoracic vertebrae.
Thus, there is a need in the art for a seat back for a vehicular seat, which is provided with a plate member for reducing or eliminating strong pushing force to the thoracic vertebrae of a user.